The present invention relates to a brake system including a brake booster as may be used as a brake for automobiles.
A brake system is known in the art which includes a pneumatic or liquid pressure operated brake booster.
By way of example, a pneumatic pressure operated brake booster comprises a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism disposed in the valve body for a switching control of flow paths therein, and an input shaft mechanically coupled to a brake pedal and adapted to drive a valve plunger, which forms part of the valve mechanism, to switch the flow path. The valve mechanism is urged by a depression force applied to the brake pedal to switch the flow path, thereby developing an output in accordance with the magnitude of the depression force.
A brake system obtains the output from the brake booster having a magnitude which depends on the magnitude of the depression force applied to the brake pedal, but a demand is sometimes placed such that the output from the brake booster can be freely controlled during the braking operation independently from an input applied to the brake booster.
For example, a brake system on a vehicle which is provided with a regenerative brake unit may be required to reduce the output from the brake booster during the braking operation independently from the input to the brake booster. Because the regenerative brake unit produces a braking effort when it is operated, it follows that if the depression force to the brake pedal is maintained constant, a variation in the braking effort produced by the regenerative brake unit results in a variation in the total braking effort, causing a driver to feel an unnaturalness.
In this instance, if the braking effect which results from the brake booster could be diminished by an amount corresponding to the braking effort produced by the regenerative brake unit as it is operated, the total braking effort could be maintained constant, avoiding the feeling of unnaturalness which the driver would experience otherwise. The same is true when an engine brake or an exhaust gas brake is operated.
On the other hand, there is also an instance where it is demanded to increase the output from the brake booster independently from the input applied to the brake pedal. This occurs, for example, with a brake system which is provided with a brake assisting apparatus that is designed to provide an increased output during a quick braking operation than during a normal braking pedal depression, thus enabling a powerless person or aged driver to perform a quick braking operation.
Another instance of demanding an increased output from the brake booster occurs when running on a down grade or with an increased payload onboard.
In this manner, there is a demand for a free control over the output of the brake booster in many instances, but the practice in the prior art has been to accommodate for such demand by employing a devoted arrangement individually from system to system, which lacks a universality. To meet the demand, an increased number of parts are required including a solenoid operated valve, a pump or the like, and are used in a complicated arrangement, which results in an increased cost.
On the other hand, there is also an instance where it is demanded to increase the output from the brake booster independently from the input applied to the brake pedal. This occurs, for example, with a brake system which is provided with a brake assisting apparatus that is designed to provide an increased output during a quick brake operation than during a normal brake pedal depression, thus enabling a powerless woman or aged driver to perform a quick brake operation.
Another instance of demanding an increased output from the brake booster occurs when running on a down grade or with an increased payload onboard.
In this manner, there is a demand for a free control over the output of the brake booster in many instances, but the practice in the prior art has been to accommodate for such demand by employing a devoted arrangement individually from system to system, which lacks a universality. To meet the demand, an increased number of parts are required including a solenoid operated valve, a pump or the like, and are used in a complicated arrangement, which results in an increased cost.
In view of the foregoing, the present invention intends to provide a brake system which permits an output from a brake booster to be freely controlled independently from a depression force applied to a brake pedal in response to a braking effort increase/decrease demand.
Specifically, in accordance with the invention, there is provided a brake system comprising a valve mechanism of a brake booster, the valve mechanism being urged in response to a depression force applied to a brake pedal to switch a flow path therein to thereby cause the brake booster to develop an output in accordance with the magnitude of the depression force, and a solenoid for urging the valve mechanism in either the same direction as or in the opposite direction from the depression force, the solenoid being responsive to a braking effort increase/decrease demand to increase/decrease the urging force applied to the valve mechanism and hence the output from the brake booster.
During a normal braking operation, the valve mechanism is urged to switch a flow path in response to the depression force applied to the brake pedal, causing an output to be developed in accordance with the magnitude of the depression force. In response to a braking effort increase demand signal, for example, the solenoid increases the urging force applied to the valve mechanism in accordance with the signal, thereby increasing the output from the brake booster.
In this manner, the urging force which is applied to the valve mechanism from the solenoid can be increased or decreased, and accordingly, if the depression force applied to the brake pedal remains constant, the output from the brake booster can be freely controlled.
Above, and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.